/* Fig. 11.16: fig11_16.c
   This program reads a random access file sequentially, updates data
   already written to the file, creates new data to be placed in the
   file, and deletes data previously in the file. */
#include <stdio.h>

/* clientData structure definition */
struct clientData { 
   int acctNum;          /* account number */
   char lastName[ 15 ];  /* account last name */
   char firstName[ 10 ]; /* account first name */
   double balance;       /* account balance */
}; /* end structure clientData */

/* prototypes */
int enterChoice( void );
void textFile( FILE *readPtr );
void updateRecord( FILE *fPtr );
void newRecord( FILE *fPtr );
void deleteRecord( FILE *fPtr );

int main()
{ 
   FILE *cfPtr; /* credit.dat file pointer */
   int choice;  /* user's choice */

   /* fopen opens the file; exits if file cannot be opened */
   if ( ( cfPtr = fopen( "credit.dat", "rb+" ) ) == NULL ) {
      printf( "File could not be opened.\n" );
   } /* end if */
   else { 

      /* enable user to specify action */
      while ( ( choice = enterChoice() ) != 5 ) { 

         switch ( choice ) { 

            /* create text file from record file */
            case 1:
               textFile( cfPtr );
               break;

            /* update record */
            case 2:
               updateRecord( cfPtr );
               break;

            /* create record */
            case 3:
               newRecord( cfPtr );
               break;

            /* delete existing record */
            case 4:
               deleteRecord( cfPtr );
               break;
         
            /* display message if user does not select valid choice */
            default:
               printf( "Incorrect choice\n" );
               break;
       
         } /* end switch */

      } /* end while */

      fclose( cfPtr ); /* fclose closes the file */
   } /* end else */
 
   return 0; /* indicates successful termination */

} /* end main */

/* create formatted text file for printing */ 
void textFile( FILE *readPtr )
{ 
   FILE *writePtr; /* accounts.txt file pointer */

   /* create clientData with default information */
   struct clientData client = { 0, "", "", 0.0 };

   /* fopen opens the file; exits if file cannot be opened */
   if ( ( writePtr = fopen( "accounts.txt", "w" ) ) == NULL ) {
      printf( "File could not be opened.\n" );
   } /* end if */
   else { 
      rewind( readPtr ); /* sets pointer to beginning of file */
      fprintf( writePtr, "%-6s%-16s%-11s%10s\n", 
         "Acct", "Last Name", "First Name","Balance" );

      /* copy all records from random-access file into text file */
      while ( !feof( readPtr ) ) { 
         fread( &client, sizeof( struct clientData ), 1, readPtr );

         /* write single record to text file */
         if ( client.acctNum != 0 ) {
            fprintf( writePtr, "%-6d%-16s%-11s%10.2f\n",
               client.acctNum, client.lastName,
               client.firstName, client.balance );
         } /* end if */

      } /* end while */

      fclose( writePtr ); /* fclose closes the file */
   } /* end else */

} /* end function textFile */

/* update balance in record */
void updateRecord( FILE *fPtr )
{ 
   int account;        /* account number */
   double transaction; /* transaction amount */

   /* create clientData with no information */
   struct clientData client = { 0, "", "", 0.0 };

   /* obtain number of account to update */
   printf( "Enter account to update ( 1 - 100 ): " );
   scanf( "%d", &account );

   /* move file pointer to correct record in file */
   fseek( fPtr, ( account - 1 ) * sizeof( struct clientData ), 
      SEEK_SET );

   /* read record from file */
   fread( &client, sizeof( struct clientData ), 1, fPtr );

   /* display error if account does not exist */
   if ( client.acctNum == 0 ) {
      printf( "Acount #%d has no information.\n", account );
   } /* end if */
   else { /* update record */
      printf( "%-6d%-16s%-11s%10.2f\n\n", 
         client.acctNum, client.lastName, 
         client.firstName, client.balance );
      
      /* request transaction amount from user */ 
      printf( "Enter charge ( + ) or payment ( - ): " );
      scanf( "%lf", &transaction );
      client.balance += transaction; /* update record balance */
      
      printf( "%-6d%-16s%-11s%10.2f\n", 
         client.acctNum, client.lastName, 
         client.firstName, client.balance );
      
      /* move file pointer to correct record in file */
      fseek( fPtr, ( account - 1 ) * sizeof( struct clientData ), 
         SEEK_SET );

      /* write updated record over old record in file */
      fwrite( &client, sizeof( struct clientData ), 1, fPtr );
   } /* end else */

} /* end function updateRecord */

/* delete an existing record */
void deleteRecord( FILE *fPtr )
{ 

   struct clientData client; /* stores record read from file */
   struct clientData blankClient = { 0, "", "", 0 }; /* blank client */
   
   int accountNum; /* account number */

   /* obtain number of account to delete */
   printf( "Enter account number to delete ( 1 - 100 ): " );
   scanf( "%d", &accountNum );

   /* move file pointer to correct record in file */
   fseek( fPtr, ( accountNum - 1 ) * sizeof( struct clientData ), 
      SEEK_SET );

   /* read record from file */
   fread( &client, sizeof( struct clientData ), 1, fPtr );

   /* display error if record does not exist */
   if ( client.acctNum == 0 ) {
      printf( "Account %d does not exist.\n", accountNum );
   } /* end if */
   else { /* delete record */

      /* move file pointer to correct record in file */
      fseek( fPtr, ( accountNum - 1 ) * sizeof( struct clientData ), 
         SEEK_SET );

      /* replace existing record with blank record */
      fwrite( &blankClient, 
         sizeof( struct clientData ), 1, fPtr );
   } /* end else */

} /* end function deleteRecord */

/* create and insert record */
void newRecord( FILE *fPtr )
{ 
   /* create clientData with default information */
   struct clientData client = { 0, "", "", 0.0 };

   int accountNum; /* account number */

   /* obtain number of account to create */
   printf( "Enter new account number ( 1 - 100 ): " );
   scanf( "%d", &accountNum );

   /* move file pointer to correct record in file */
   fseek( fPtr, ( accountNum - 1 ) * sizeof( struct clientData ), 
      SEEK_SET );

   /* read record from file */
   fread( &client, sizeof( struct clientData ), 1, fPtr );

   /* display error if account already exists */
   if ( client.acctNum != 0 ) {
      printf( "Account #%d already contains information.\n",
              client.acctNum );
   } /* end if */
   else { /* create record */

      /* user enters last name, first name and balance */
      printf( "Enter lastname, firstname, balance\n? " );
      scanf( "%s%s%lf", &client.lastName, &client.firstName, 
         &client.balance );

      client.acctNum = accountNum;
      
      /* move file pointer to correct record in file */
      fseek( fPtr, ( client.acctNum - 1 ) * 
         sizeof( struct clientData ), SEEK_SET );

      /* insert record in file */
      fwrite( &client, 
         sizeof( struct clientData ), 1, fPtr );
   } /* end else */

} /* end function newRecord */

/* enable user to input menu choice */
int enterChoice( void )
{ 
   int menuChoice; /* variable to store user's choice */

   /* display available options */
   printf( "\nEnter your choice\n"
      "1 - store a formatted text file of acounts called\n"
      "    \"accounts.txt\" for printing\n"
      "2 - update an account\n"
      "3 - add a new account\n"
      "4 - delete an account\n"
      "5 - end program\n? " );

   scanf( "%d", &menuChoice ); /* receive choice from user */

   return menuChoice;

} /* end function enterChoice */



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 * (C) Copyright 1992-2004 by Deitel & Associates, Inc. and               *
 * Pearson Education, Inc. All Rights Reserved.                           *
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